SAN JOSE — A gunman who killed nine co-workers at a Northern California rail yard shot himself twice in the head as sheriff’s deputies raced into a building, according to authorities who on Tuesday released body-camera footage of the tense encounter.

The nearly 4 1/2 minutes of footage is from one deputy who arrived minutes after the first shooting reports and while shots were still being fired at the Santa Clara Valley Transportation Authority bus and rail yard in San Jose, where 57-year-old Samuel Cassidy opened fire before killing himself.

Video Shows Contact Team Finding Gunman Dead

A “contact team” of deputies and San Jose police officers was immediately formed to find the gunman, who was reported to be inside a building and armed with a handgun. The body camera footage shows the team cautiously climbing stairs to the third floor, where a VTA supervisor comes out with arms raised and hands over his keycard so officers can get inside the building.

The five-member team then sweeps into the building, guns raised, using gun-mounted flashlights as they pass through rooms and corridors to a dispatch center.

Within minutes, they hear a gunshot, then another, followed by two more. As they come to another door, one of the team looks through a small window and says: “I’ve got somebody down” inside. The team opens the door and somebody shouts “Let me see your hands!”

What might be two more shots are heard.

The footage shows a man slumped in a chair near a stairwell with a gun in his hand. He is across from a dispatch center door with a window shattered by gunfire.

The gunman had shot himself under the chin then put the gun to the side of his head, the sheriff said.

It wasn’t clear whether Cassidy knew that law enforcement officers were closing in on him or not, but he may have seen their flashlights and heard them yelling to each other as they determined where the shooter and victims were as they moved through the building, Smith said.

Deputies and Officers Had Active Shooter Protocol Training

Smith said her office used an active shooter protocol advocated by a lieutenant who had been in Colorado during the 1999 Columbine school mass shooting there. Smith said law enforcement had been training together.

The deputies and officers “hardly spoke a word to each other” when they entered the building because “they knew what their job was,” she said, adding that they showed extraordinary courage.

“There were over 100 VTA employees on site that morning, and I believe the bravery of all of law enforcement personnel really prevented the loss of additional life,” she said.

A VTA spokeswoman told the Mercury News in San Jose that it may take weeks or months to resume service on the commuter rail line. The Guadalupe Yard operates as the nerve center of the light rail network and is now a crime scene under sheriff’s department control. Spokeswoman Stacey Hendler Ross said the agency is focused on supporting traumatized workers who lost colleagues.

The footage was released as a new FBI report finds that California had the most mass shooting incidents in the last 20 years, a figure that aligns with its population, the report found. It also came as an off-duty Los Angeles County firefighter fatally shot and killed one colleague and injured another before taking his own life.

The sheriff said investigators were still trying to determine the motive for the shootings, although acquaintances and his ex-wife said Cassidy had talked about hating his job at least a decade ago and had an angry and unpredictable streak.

“We’re beginning to piece things together. But we’ve talked with hundreds of witnesses,” Smith said.